JP 2011-053102A proposes a control system for controlling a brushless motor, for example. This conventional control system includes a control circuit, which outputs a rotation command signal to a driving circuit for driving a brushless motor. The control circuit generates a pulse signal having a frequency corresponding to a set rotation speed of the motor and outputs it to the driving circuit. The driving circuit drives the motor in response to the pulse signal inputted from the control circuit.
In the conventional control system described above, the pulse signal is outputted from an open-collector or an open-drain (collectively referred to as open-collector below), for example, when a rotation detection pulse is generated. The rotation detection pulse is generated in response to a signal change in a signal transmission line connected to the open-collector by turning on and off a transistor.
In this operation, it is repeated that a current flows in the signal transmission line when the transistor is turned on and the current does not flow in the signal transmission line when the transistor is turned off. For this reason, a current change arises in the signal transmission line and radiates an unnecessary electromagnetic wave as radio noise. It is thus required to reduce radiation of the unnecessary electromagnetic wave in compliance with recent regulation on unnecessary electromagnetic radiation.
At a contact of a connector, a contaminant film such as an oxide film is formed as use environment changes for the worse and use period increases. It is required to supply a current in excess of a sufficient amplitude for preventing the contaminant film from being formed and breaking the contaminant film already formed, so that quality of the contact of the connector may be maintained.
It is thus desired to lower the current amplitude level of a pulse current for reducing radiation of the unnecessary electromagnetic wave, It is also desired to increase the current amplitude level for maintaining the quality of the contact of the connector without significant deterioration.